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My
research
focuses on the coupled biogeochemical cycles of carbon, oxygen and
water in the terrestrial biosphere.
We
have a good mechanistic understanding of gas exchange at the
cell/leaf scale and extensive data on carbon cycling at the global
scale. But there is a gap in quantifying carbon and water cycles on the
intermediate scales. I am working on methods to close this gap with a
combination of modelling and experiments from small (leaf) to
intermediate (ecosystem) and large (global) scales.
Stable
isotopes are important research tools in this context. The
isotopic signatures of atmospheric gases provide independent tracers
that allow to separate the effects of physical transport from
biological activity. The power of combining different tracers is that
each is adding constraints on processes, pools and fluxes. For example,
the cycles of carbon and water are linked at their parallel pathways
through the stomata of leaves. The isotopic signature of foliage water
affects those of carbon dioxide and oxygen during photosynthetic gas
exchange. At the larger scale, the isotopic signature of atmospheric
oxygen (Dole-Morita effect), a tracer of global biospheric activity,
provides a link to the past: it can be measured in air bubbles enclosed
in polar ice cores over glacial-interglacial cycles.
In 2008, we developed a coupled model for exploring the sensitivity
of relative trends in plant water use efficiency (WUE) and carbon
isotope signatures (13C discrimination, d13C of organic material) to
changes in environmental conditions and leaf functional traits (Seibt
et al. (2008) Carbon isotopes and water use efficiency - sense and
sensitivity). The model versions, list of parameters, and example
plots are available at: Carbon isotopes and
water use efficiency (updated link).
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branch chambers
soil chambers
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Hainich, Germany
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Griffin, Scotland
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boundary layer sampling
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collection of flask samples
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